With the fast development of automobile, national defense, aviation, aerospace and other industries as well as the application of new materials like aluminum alloy, there are increasingly high requirements on combined machine tools. As taking typical parts in aviation industry, such as a turbine case and a fan case, for example, turning, milling, radial drilling and boring and other machining operations are required simultaneously in the process for such parts, and high precision is needed. Therefore, a workpiece needs to be positioned, clamped and set with respect to cutters repeatedly among a plurality of machine tools during actual machining, which would cause time waste and reduce production efficiency, and plenty of unnecessary errors are generated midway due to the continuous replacement and adjustment of cutters. The production efficiency and the machining precision must be improved remarkably if these functions are integrated.
Meanwhile, in mechanical transmission technologies of the prior art, a motor rotates to generate power, and the power is enlarged by mechanical transmission elements, such as a transmission case, a reduction gearbox, a guide screw and a worm gear, and then is transmitted to an executing part, whereby the machine operates. While functions that a lot of traditional machine tools fail to achieve have been achieved by applying these mechanical transmission technologies to key parts of a machine tool, such as a C-axis rotating machine tool work table and a B-axis pendulum machine tool milling head and the like, these technologies functioning simply by mechanical transmission could not keep pace with the development of modern international machine tool manufacturing industry in the aspects of speed, precision and service life.
In addition, a majority of the complex multi-axis machine tools at home and abroad adopt a single driving center driving, i.e. one ball screw, for driving key functional parts, such as a uniaxial rotating work table, but in this kind of structure, a driving force cannot act upon the gravity center of a moving member accurately during the machining course. Therefore, there is a tendency to generate a twisting motion under high cutting speed, especially under large feeding speed and high rotating speed of a rotating table. This unavoidable twisting motion and the effect of inertia generated by the moving member is to lead to the vibration of the machine tool, which causes machine tool members, such as castings including a machine tool bed body or stand columns and the like, to be bent or deformed, and affects the precision and service life of the rotating table to a certain extent.
On the other hand, it has been found in accordance with the investigation on the current common vertical complex machining centers on the market that a pendulum head used in a traditional vertical complex turning and milling cannot enter the deep inside of a part for machining owing to limitations in the structure and dimension thereof, and a traditional vertical lathe is incapable of performing milling work. The machining requirements of the parts like a turbine case could be satisfied if these two functions are integrated.
Furthermore, with the development of manufacturing industry and increasingly fierce competitions, the machining requirement of parts becomes more complex. With respect to the machining of some large cavity-type parts turning, milling and drilling are required at the same time. During actual machining, a workpiece needs to be moved among vertical lathe, milling machine and drilling machine and be set with respect to the cutters, which results in low utilization rate of the machine tools, greatly increases the machining-assisting time and the errors due thereto owing to complex operations, and affects the machining efficiency and precision negatively. All the present power heads or angle heads on the market depend on machining power transmission via a machine tool spindle, and accordingly, cannot be applied to a vertical lathe like structure that is not provided with a cutter rotating machining function. However, the contradiction lies in the fact that this vertical lathe like structure most urgently requires milling and drilling machining.